1. Field of the Invention
The present invention relates to a ferroelectric capacitor which shows less fatigue and is suitable as a large-capacity nonvolatile memory, a process for efficiently producing the ferroelectric capacitor, and a high-performance semiconductor device having the ferroelectric capacitor.
2. Description of the Related Art
Ferroelectrics have excellent ferroelectricity, piezoelectricity and pyroelectricity and are widely used in, for example, a variety of memories, actuators, and sensors. For example, such ferroelectrics have been applied to nonvolatile memories by utilizing the hysteresis of the ferroelectrics. Certain ferroelectric capacitors comprising a lower electrode, a ferroelectric, and an upper electrode arranged in this order on a substrate are known as nonvolatile memories.
Pb-containing materials such as Pb(Zr,Ti)O3 [PZT] having excellent ferroelectricity have been suitably used as materials for the ferroelectrics. These ferroelectrics may be formed, for example, by a sol-gel method, sputtering or metalorganic chemical vapor deposition (MOCVD). Among them, the metalorganic chemical vapor deposition (MOCVD) has been often employed, since it can yield ferroelectric crystals which exhibit high ferroelectricity even when finely divided and have a high density while it also provides a good step coverage. Such a ferroelectric capacitor has been conventionally formed by forming a lower electrode with the use of a noble metal such as Pt or Ir or an electrically conductive oxide such as IrOx, wherein x is more than 0 and is 2 or less; forming a ferroelectric film of lead zirconate titanate (PZT) on the lower electrode by MOCVD; and forming an upper electrode on the ferroelectric film.
However, when the ferroelectric capacitor having the thus-formed ferroelectric is applied to a nonvolatile memory and the ferroelectric undergoes repetitive switching process (repetitive polarization reversal), it induces “fatigue (polarization fatigue)” in which the polarization of the ferroelectric decreases. To reduce the “fatigue”, i.e., to improve fatigue properties, Japanese Patent Application Laid-Open (JP-A) Nos. 10-173141, 2001-144264, 2001-267518, and 2002-100740 each propose the use of an oxide electrode in the ferroelectric capacitor. Another attempt has been made to form a ferroelectric capacitor having an IrO2/PZT/Ir multilayer structure by MOCVD, but the resulting ferroelectric capacitor does not have sufficiently improved fatigue properties.